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Abstract:

A pretensioner comprising a gas generating unit; a pretensioner body to
whose inside the gas is supplied; a spool driving member disposed inside
the pretensioner body and causing a spool to rotate to retract webbing
onto the spool; a gas flow rate adjusting portion disposed in the spool
driving member and whose inner peripheral shape is set in accordance with
a flow rate of the gas to be passed through the gas flow rate adjusting
portion; and a filter unit having a vent portion that is communicated
with a space between the gas generating unit and the spool driving member
and is also communicated with the gas flow rate adjusting portion. The
open shape of the gas flow rate adjusting portion has a portion that does
not coincide in a plan view with the open shape of the vent portion, and
the overall open area of the vent portion is set larger than the open
area of the gas flow rate adjusting portion.

Claims:

1. A pretensioner comprising: a gas generating unit which, when actuated,
causes an agent to combust to thereby generate a gas; a pretensioner body
to which the gas generating unit is attached and to whose inside the gas
that has been generated by the gas generating unit is supplied; a spool
driving member that is disposed inside the pretensioner body, is caused
to move by the pressure of the gas that has been supplied to the inside
of the pretensioner body, and by this movement causes a spool to rotate
to thereby cause webbing to be retracted onto the spool; a gas flow rate
adjusting portion that is disposed in the spool driving member, a gas
passage direction downstream side of the gas flow rate adjusting portion
communicating with an opposite side of a gas generating unit side with
respect to the spool driving member, and whose inner peripheral shape is
set in accordance with a flow rate of the gas to be passed through the
gas flow rate adjusting portion; and a filter unit that has, or forms, a
vent portion that is communicated with a space between the gas generating
unit and the spool driving member and is also communicated with the gas
flow rate adjusting portion, wherein an open shape of the gas flow rate
adjusting portion and an open shape of the vent portion are set in such a
way that the open shape of the gas flow rate adjusting portion has a
portion that does not coincide in a plan view with the open shape of the
vent portion, and the overall open area of the vent portion is set larger
than the open area of the gas flow rate adjusting portion.

2. The pretensioner according to claim 1, wherein a setting range of the
vent portion is set larger than a setting range of the gas flow rate
adjusting portion.

3. The pretensioner according to claim 1, wherein a plurality of the vent
portion are disposed, the respective open areas of the vent portions are
set smaller than the open area of the gas flow rate adjusting portion,
and a sum total of the open areas of all of the vent portions is set
larger than the open area of the gas flow rate adjusting portion.

4. The pretensioner according to claim 1, further comprising an
attachment hole that is formed in the spool driving member on a gas
passage direction upstream side of the gas flow rate adjusting portion,
with the attachment hole having an end portion on the gas passage
direction upstream side that opens larger than the open area of the gas
flow rate adjusting portion and an end portion on the gas passage
direction downstream side that is communicated with the gas flow rate
adjusting portion, wherein the filter unit is attached to the attachment
hole in such a way as to be inscribed in an inner peripheral portion of
the attachment hole, and the vent portion that opens at both gas passage
direction end portions of the filter unit attached to the attachment hole
is formed in the filter unit.

5. The pretensioner according to claim 1, further comprising an
attachment hole that is formed in the spool driving member on a gas
passage direction upstream side of the gas flow rate adjusting portion,
with the attachment hole having an end portion on the gas passage
direction upstream side that opens larger than the open area of the gas
flow rate adjusting portion and an end portion on the gas passage
direction downstream side that is communicated with the gas flow rate
adjusting portion, wherein the filter unit is attached to the attachment
hole in such a way as to be inscribed in an inner peripheral portion of
the attachment hole, an outer peripheral shape of the filter unit is
capable of being inscribed in the inner peripheral portion of the
attachment hole and differs from an inner peripheral shape of the
attachment hole, and a gap formed between the inner peripheral portion of
the attachment hole and an outer periphery of the filter unit is used as
the vent portion.

6. The pretensioner according to claim 1, further comprising an
attachment hole that is formed in the spool driving member on a gas
passage direction upstream side of the gas flow rate adjusting portion,
with the attachment hole having an end portion on the gas passage
direction upstream side that opens larger than the open area of the gas
flow rate adjusting portion and an end portion on the gas passage
direction downstream side that is communicated with the gas flow rate
adjusting portion, wherein a plug whose outer peripheral shape is formed
in a shape differing from an inner peripheral shape of the attachment
hole and which is inserted into and held in the attachment hole is used
as the filter unit, and the plug has an insertion portion where at least
part of a gap formed between an outer peripheral portion of the insertion
portion and an inner peripheral portion of the attachment hole is
communicated with the gas flow rate adjusting portion and a head portion
that is positioned on the gas generating unit side of the spool driving
member in a state where the insertion portion has been inserted into the
attachment hole, with an opening formed in an outer peripheral surface of
the head portion being communicated with the gap between the inner
peripheral portion of the attachment hole and the outer peripheral
portion of the insertion portion.

7. The pretensioner according to claim 6, wherein the plug includes an
insertion portion body, part of whose outer periphery contacts the inner
peripheral portion of the attachment hole in a state where the insertion
portion body has been inserted into the attachment hole, and a small
diameter portion whose outer peripheral shape is formed slenderer than
that of the insertion portion body on the side of the insertion portion
body opposite the head portion side.

8. The pretensioner according to claim 1, wherein the filter unit is
disposed on the gas generating unit side with respect to an end portion
of the spool driving member, the gas flow rate adjusting portion is
communicated with a space between the end portion of the spool driving
member on the gas generating units side and the filter unit, and the vent
portion is formed in the filter unit.

9. The pretensioner according to claim 1, wherein the filter unit is
disposed on the gas generating unit side with respect to an end portion
of the spool driving member, a gap between an outer peripheral portion of
the end portion of the spool driving member on the gas generating unit
side and an outer peripheral portion of the filter unit is used as the
vent portion, and the gas flow rate adjusting portion is communicated
with a space between the end portion of the spool driving member on the
gas generating units side and the filter unit.

10. The pretensioner according to claim 1, wherein disposed in the spool
driving member are a driving member body whose outer peripheral shape is
smaller than the inner peripheral shape of the pretensioner body, an
annular member that is attached to the driving member body in such a way
as to surround an outer peripheral portion of the driving member body and
whose inner peripheral portion contacts the outer peripheral portion of
the driving member body in a state where the annular member has been
attached to the driving member body, a groove portion that is formed in
the outer peripheral portion of the driving member body, opens at an end
portion of the driving member body on the gas generating units side and
the outer peripheral portion of the driving member body, is communicated
with the gas flow rate adjusting portion, and is spaced apart from the
inner peripheral portion of the annular member in a state where the
annular member has been attached to the driving member body is used as
the vent portion, and the driving member body and the annular member are
used as the filter unit.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under 35 USC 119 from Japanese
Patent Applications No. 2010-285911 filed on Dec. 22, 2010, and No.
2011-176102 filed on Aug. 11, 2011, the disclosures of which are
incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates to a pretensioner that configures a
seat belt device of a vehicle.

[0004] 2. Related Art

[0005] The pretensioner disclosed in Japanese Patent Application Laid-Open
(JP-A) No. 2009-241863 is equipped with a piston that is slidable inside
a cylinder. When the piston is caused to slide by the pressure of a gas
that has been generated as a result of a gas generator attached to the
cylinder being actuated, a rack bar integrated with the piston causes a
pinion to rotate, a spool is rotated in a retraction direction by the
rotation of the pinion, and webbing is retracted onto the spool.

SUMMARY

[0006] Incidentally, when detaching a seat belt device that has become
unnecessary from a vehicle, it is preferred that the gas inside the
cylinder of the pretensioner be let out beforehand. Therefore, it may be
preferable to dispose a small hole for letting out the gas in the piston
when, for example, when a seat belt device is manufactured.

[0007] However, if the inner diameter dimension of the small hole is too
small, it is easy for the small hole to become clogged with cinders of
the agent that was combusted in order to generate the gas. Conversely, if
the inner diameter dimension of the small hole is too large, the gas ends
up escaping unnecessarily in a state where the pretensioner is operating.
In this way, setting the shape of the hole for letting out the gas has
been difficult.

[0008] In view of the above-described circumstances, the present invention
obtains a pretensioner that can effectively suppress clogging resulting
from cinders of an agent and in which a gas does not escape
unnecessarily.

[0009] A pretensioner of a first aspect of the invention includes: a gas
generating unit which, when actuated, causes an agent to combust to
thereby generate a gas; a pretensioner body to which the gas generating
unit is attached and to whose inside the gas that has been generated by
the gas generating unit is supplied; a spool driving member that is
disposed inside the pretensioner body, is caused to move by the pressure
of the gas that has been supplied to the inside of the pretensioner body,
and by this movement causes a spool to rotate to thereby retracting
webbing onto the spool; a gas flow rate adjusting portion that is
disposed in the spool driving member, a gas passage direction downstream
side of the gas flow rate adjusting portion communicating with an
opposite side of a gas generating unit side with respect to the spool
driving member, and whose inner peripheral shape is set in accordance
with the flow rate of the gas to be passed through the gas flow rate
adjusting portion; and a filter unit that has, or forms, a vent portion
that is communicated with a space between the gas generating unit and the
spool driving member and is also communicated with the gas flow rate
adjusting portion. An open shape of the gas flow rate adjusting portion
and an open shape of the vent portion are set in such a way that the open
shape of the gas flow rate adjusting portion does not coincide in a plan
view with the open shape of the vent portion, and the overall open area
of the vent portion is set larger than the open area of the gas flow rate
adjusting portion.

[0010] In the pretensioner of the first aspect, the gas is generated when
the gas generating unit is actuated and the agent disposed in the gas
generating unit combusts, and the gas is supplied to the pretensioner
body. When the gas is supplied to the pretensioner body, the spool
driving member inside the pretensioner body is caused to move by the
pressure of the gas. Because of this, the spool rotates in a retraction
direction and retracts the webbing from the proximal end side of the
webbing.

[0011] The gas flow rate adjusting portion is formed in the spool driving
member. The gas passage direction downstream side of the gas flow rate
adjusting portion communicates with the opposite side of the gas
generating unit side with respect to the spool driving member. Further,
the gas flow rate adjusting portion is communicated with the vent portion
of the filter unit.

[0012] The vent portion is communicated with the space between the gas
generating unit and the spool driving member inside the pretensioner
body, and the gas between the gas generating unit and the spool driving
member inside the pretensioner body can pass through the vent portion of
the filter unit and the gas flow rate adjusting portion and escape to the
side of the spool driving member opposite the gas generating unit side.
Consequently, after the actuation of the pretensioner has ended, the gas
escapes to the side of the spool driving member opposite the gas
generating unit side, whereby the high-pressure state between the gas
generating unit and the spool driving member inside the pretensioner body
can be eliminated.

[0013] Further, as described above, the gas escapes via the gas flow rate
adjusting portion and the vent portion of the filter unit to the side of
the spool driving member opposite the gas generating unit side, but the
open shape of the gas flow rate adjusting portion is set in such a way
that, for example, the flow rate of the gas becomes such that there is no
hindrance with respect to causing the spool to rotate to retract the
webbing. Consequently, the pressure of the gas that has been supplied to
the pretensioner body can cause the spool to retract the webbing so that
the body of the vehicle occupant can be restrained more strongly than
before.

[0014] When the gas that has been generated by the gas generating unit is
supplied to the inside of the pretensioner body, cinders of the agent
that was combusted in order to generate the gas are also sent into the
inside of the pretensioner body. In the pretensioner of the first aspect,
the shape of the vent portion and the shape of the gas flow rate
adjusting portion are set in such a way that, in a case where the setting
range of the vent portion and the open shape of the gas flow rate
adjusting portion are seen superimposed in a plan view, the open shape of
the vent portion and the open shape of the gas flow rate adjusting
portion do not coincide. Moreover, the overall open area of the vent
portion on the gas entrance side is set larger than the open area of the
gas flow rate adjusting portion, so an opening remains even if part of
the vent portion becomes blocked by the cinders of the agent.

[0015] Consequently, even in this state the gas with the flow rate which
is set according to the gas flow rate adjusting portion can be caused to
flow into the vent portion from the outer sides of the cinders and can
pass through the vent portion and the gas flow rate adjusting portion and
escape to the side of the spool driving member opposite the gas
generating unit side inside the pretensioner body. Because of this, the
high-pressure state between the gas generating unit and the spool driving
member inside the pretensioner body can be effectively eliminated.

[0016] In a pretensioner of a second aspect of the invention, in the first
aspect, a setting range of the vent portion may be set larger than a
setting range of the gas flow rate adjusting portion.

[0017] In the pretensioner of the second aspect, the setting range of the
vent portion is larger than the setting range of the gas flow rate
adjusting portion. For this reason, even if cinders of the agent of a
size that can pass through the gas flow rate adjusting portion block a
part of the vent portion, remaining part of the vent portion is open.

[0018] In a pretensioner of a third aspect of the invention, in the first
aspect or the second aspect, plurality of the vent portions may be set,
the respective open areas of the vent portions may be set smaller than
the open area of the gas flow rate adjusting portion, and a sum total of
the open areas of all of the vent portions may be set larger than the
open area of the gas flow rate adjusting portion.

[0019] According to the pretensioner of the third aspect, the individual
open areas of the plurally set vent portions is set to become smaller
than the open area of the gas flow rate adjusting portion and in such a
way that the sum total of the open areas of the vent portions becomes
larger than the open area of the gas flow rate adjusting portion.

[0020] For this reason, even if the cinders of the agent become caught on
the filter unit, the difference between the sum total of the open areas
of the vent portions without the cinders and the open area of the gas
flow rate adjusting portion becomes somewhat smaller, but a sufficient
quantity of the gas can be caused to pass through to the gas flow rate
adjusting portion side.

[0021] In a pretensioner of a fourth aspect of the invention, in the first
aspect to the third aspect, the pretensioner further includes an
attachment hole that is formed in the spool driving member on a gas
passage direction upstream side of the gas flow rate adjusting portion.
The attachment hole has an end portion on the gas passage direction
upstream side that opens larger than the open area of the gas flow rate
adjusting portion and an end portion on the gas passage direction
downstream side that is communicated with the gas flow rate adjusting
portion, and the filter unit is attached to the attachment hole in such a
way as to be inscribed in an inner peripheral portion of the attachment
hole. Moreover, the vent portion that opens at both gas passage direction
end portions of the filter unit attached to the attachment hole is formed
in the filter unit.

[0022] According to the pretensioner of the fourth aspect, the attachment
hole is formed on the gas passage direction upstream side of the gas flow
rate adjusting portion in the spool driving member. The attachment hole
is communicated with the gas flow rate adjusting portion. Further, the
end portion of the attachment hole on the gas passage direction upstream
side opens larger than the open area of the gas flow rate adjusting
portion. The filter unit is attached to the attachment hole. The vent
portion is formed in the filter unit, and the vent portion opens at both
gas passage direction end portions of the filter unit attached to the
attachment hole.

[0023] By giving the pretensioner this configuration, it suffices simply
to attach the filter unit in which the vent portion has been formed
beforehand to the attachment hole, so the configuration can be made
simple

[0024] In a pretensioner of a fifth aspect of the invention, in the first
aspect or the second aspect, the pretensioner further includes an
attachment hole that is formed in the spool driving member on a gas
passage direction upstream side of the gas flow rate adjusting portion.
The attachment hole has an end portion on the gas passage direction
upstream side that opens larger than the open area of the gas flow rate
adjusting portion and an end portion on the gas passage direction
downstream side that is communicated with the gas flow rate adjusting
portion. An outer peripheral shape of the filter unit is capable of being
inscribed in an inner peripheral portion of the attachment hole and
differs from an inner peripheral shape of the attachment hole, and a gap
formed between the inner peripheral portion of the attachment hole and an
outer periphery of the filter unit is used as the vent portion.

[0025] According to the pretensioner of the fifth aspect, the attachment
hole is formed on the gas passage direction upstream side of the gas flow
rate adjusting portion in the spool driving member. The attachment hole
is communicated with the gas flow rate adjusting portion. Further, the
end portion of the attachment hole on the gas passage direction upstream
side opens larger than the open area of the gas flow rate adjusting
portion.

[0026] The filter unit is attached to the attachment hole. Here, the outer
peripheral shape of the filter unit is a shape that is inscribed in the
inner peripheral portion of the attachment hole but differs from the
inner peripheral shape of the attachment hole. For this reason, when the
filter unit is attached to the attachment hole, a gap is formed between
the inner peripheral portion of the attachment hole and the outer
peripheral portion of the filter unit, and the gap becomes the vent
portion.

[0027] In a pretensioner of a sixth aspect of the invention, in the first
aspect to the fifth aspect, the pretensioner further includes an
attachment hole that is formed in the spool driving member on a gas
passage direction upstream side of the gas flow rate adjusting portion.
The attachment hole has an end portion on the gas passage direction
upstream side that opens larger than the open area of the gas flow rate
adjusting portion and an end portion on the gas passage direction
downstream side that is communicated with the gas flow rate adjusting
portion. A plug whose outer peripheral shape is formed in a shape
differing from an inner peripheral shape of the attachment hole and which
is inserted into and held in the attachment hole is used as the filter
unit. The plug has: an insertion portion where at least part of a gap
formed between an outer peripheral portion of the insertion portion and
an inner peripheral portion of the attachment hole is communicated with
the gas flow rate adjusting portion; and a head portion that is
positioned on the gas generating unit side of the spool driving member in
a state where the insertion portion has been inserted into the attachment
hole. An opening formed in an outer peripheral surface of the head
portion is communicated with the gap between the inner peripheral portion
of the attachment hole and the outer peripheral portion of the insertion
portion.

[0028] According to the pretensioner of the sixth aspect, the attachment
hole is formed on the gas passage direction upstream side of the gas flow
rate adjusting portion in the spool driving member. The attachment hole
is communicated with the gas flow rate adjusting portion at the end
portion of the attachment hole on the gas passage direction downstream
side. A plug serving as filter unit is attached to the attachment hole.

[0029] The plug has the insertion portion, and the insertion portion which
is inserted into the attachment hole. The outer peripheral shape of the
insertion portion is set in such a way that part of the outer periphery
of the insertion portion comes into contact with the inner peripheral
portion of the attachment hole, and in a state where part of the outer
periphery of the insertion portion has come into contact with the inner
peripheral portion of the attachment hole, the insertion portion--and
therefore the plug--is held in the inner peripheral portion of the
attachment hole (that is, the spool driving member) by friction between
part of the outer periphery of the insertion portion and the inner
peripheral portion of the attachment hole. Consequently, in the
pretensioner pertaining to the present invention, the plug (that is, the
filter unit) can be attached to the spool driving member simply by
inserting the insertion portion into the attachment hole.

[0030] Here, the outer peripheral shape of the insertion portion is set to
be different from the inner peripheral portion of the attachment hole.
Consequently, at the portion of the outer peripheral portion of the
insertion portion, the outer peripheral portion is spaced apart from the
inner peripheral portion of the attachment hole, and the gap is formed
between the outer peripheral portion of the insertion portion and the
inner peripheral portion of the attachment hole.

[0031] Further, the head portion is formed on the insertion portion that
is inserted into the attachment hole in this way. The head portion is
positioned on the gas generating unit side of the spool driving member in
a state where the insertion portion has been inserted into the attachment
hole, and the opening formed in the outer peripheral portion of the head
portion is communicated with the gap between the outer peripheral portion
of the insertion portion and the inner peripheral portion of the
attachment hole. At least part of the gap is communicated with the gas
flow rate adjusting portion, so the gas flows into the gap between the
outer peripheral portion of the insertion portion and the inner
peripheral portion of the attachment hole from the opening formed in the
outer peripheral portion of the head portion, and further passes through
the gas flow rate adjusting portion.

[0032] When claim 6 depends from claim 4 or 5, the gap between the outer
peripheral portion of the insertion portion and the inner peripheral
portion of the attachment hole may correspond to the vent portion. When
claim 6 depends from any one of claims 1 to 3, the gap between the outer
peripheral portion of the insertion portion and the inner peripheral
portion of the attachment hole does not necessarily correspond to the
vent portion but the opening formed in the outer peripheral surface of
the head portion may correspond to the vent portion.

[0033] In a pretensioner of a seventh aspect of the invention, in the
sixth aspect, the plug is configured to include: an insertion portion
body, part of whose outer periphery contacts the inner peripheral portion
of the attachment hole in a state where the insertion portion body has
been inserted into the attachment hole; and a small diameter portion
whose outer peripheral shape is formed slenderer than that of the
insertion portion body on the side of the insertion portion body opposite
the head portion side.

[0034] In the pretensioner of the seventh aspect, the insertion portion of
the plug is configured to include the insertion portion body and the
small diameter portion. The small diameter portion is formed on the side
of the insertion portion body opposite the head portion side. When the
insertion portion of the plug is inserted into the attachment hole, the
small diameter portion is inserted into the attachment hole before the
insertion portion body. Here, the outer peripheral shape of the small
diameter portion is slenderer and is easier to insert into the attachment
hole than the insertion portion body. Consequently, first the small
diameter portion is inserted into the attachment hole, whereby next the
insertion portion body can be easily inserted into the attachment hole.

[0035] In a pretensioner of an eighth aspect of the invention, in the
first aspect to the third aspect, the filter unit is disposed at the gas
generating unit side of an end portion of the spool driving member, the
gas flow rate adjusting portion is communicated with a space between the
end portion of the spool driving member on the gas generating unit side
and the filter unit, and the vent portion is formed in the filter unit.

[0036] According to the pretensioner of the eighth aspect, the filter unit
is disposed with respect to the spool driving member on the gas
generating unit side of the end portion of the spool driving member. The
vent portion is formed in the filter unit. The gas flow rate adjusting
portion is communicated with the space between the filter unit of this
configuration and the spool driving member, and the gas that has passed
through the vent portion formed in the filter unit passes between the
filter unit and the spool driving member and further passes through the
gas flow rate adjusting portion.

[0037] In a pretensioner of a ninth aspect of the invention, in the first
aspect to the third aspect and the eighth aspect, the filter unit is
disposed with respect to the spool driving member on the gas generating
unit side of an end portion of the spool driving member, a gap between an
outer peripheral portion of the end portion of the spool driving member
on the gas generating unit side and an outer peripheral portion of the
filter unit is used as the vent portion, and the gas flow rate adjusting
portion is communicated with a space between the end portion of the spool
driving member on the gas generating unit side and the filter unit.

[0038] According to the pretensioner of the ninth aspect, the filter unit
is disposed with respect to the spool driving member on the gas
generating unit side of the end portion of the spool driving member. The
space between the outer peripheral portion of the filter unit and the
outer peripheral portion of the end portion of the spool driving member
on the gas generating unit side is used as the vent portion, and the gas
that has passed between the outer peripheral portion of the filter unit
and the end portion of the spool driving member on the gas generating
unit side further passes through the gas flow rate adjusting portion.

[0039] In the pretensioner of the ninth aspect, as described above, the
space between the outer peripheral portion of the filter unit and the
outer peripheral portion of the end portion of the spool driving member
on the gas generating unit side is used as the vent portion, and the
cinders of the agent become caught without being able to pass between the
outer peripheral portion of the filter unit and the outer peripheral
portion of the end portion of the spool driving member on the gas
generating unit side.

[0040] Even in a state where the cinders have become caught between the
outer peripheral portion of the filter unit and the outer peripheral
portion of the end portion of the spool driving member in this way, the
gas can pass between the outer peripheral portion of the filter unit and
the outer peripheral portion of the end portion of the spool driving
member where the cinders are not caught.

[0041] In a pretensioner of a tenth aspect of the invention, in the first
aspect to the third aspect, disposed in the spool driving member are: a
driving member body whose outer peripheral shape is smaller than the
inner peripheral shape of the pretensioner body; an annular member that
is attached to the driving member body in such a way as to surround an
outer peripheral portion of the driving member body and whose inner
peripheral portion contacts the outer peripheral portion of the driving
member body in a state where the annular member has been attached to the
driving member body. A groove portion that opens at an end portion of the
driving member body on the gas generating unit side and the outer
peripheral portion of the driving member body and is communicated with
the gas flow rate adjusting portion is formed in the outer peripheral
portion of the driving member body. The groove portion that is spaced
apart from the inner peripheral portion of the annular member in a state
where the annular member has been attached to the driving member body is
used as the vent portion, and the driving member body and the annular
member are used as the filter unit.

[0042] According to the pretensioner of the tenth aspect, the outer
peripheral shape of the driving member body configuring the spool driving
member is set smaller than the inner peripheral shape of the pretensioner
body, and the annular member is attached to the outer peripheral portion
of the driving member body.

[0043] Here, the groove portion that opens at the outer peripheral portion
of the driving member body and also opens at the end portion of the
driving member body on the gas generating unit side is formed as the vent
portion of the driving member body. As described above, when the annular
member is attached to the driving member body, the outer peripheral
portion of the driving member body comes into contact with the inner
peripheral portion of the annular member, but the groove portion does not
come into contact with the inner peripheral portion of the annular
member, and for this reason the opening of the groove portion at the
outer peripheral portion of the driving member body becomes closed by the
annular member.

[0044] The gas that has flowed in to the inner side of the groove portion
from the opening of the groove portion on the gas generating unit side of
the driving member body heads toward the gas flow rate adjusting portion
that is communicated with respect to the groove portion.

[0045] As described above, the pretensioner pertaining to the present
invention can effectively suppress clogging of a vent portion resulting
from cinders of an agent and can discharge gas. Moreover, a lot of gas
can be prevented from escaping unnecessarily at the time when the
pretensioner is actuated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of exemplary examples of the present invention will be
described in detail based on the following figures, wherein:

[0047]FIG. 1 is a side view of a pretensioner pertaining to a first
embodiment;

[0048]FIG. 2 is an enlarged exploded perspective view of configurations
of relevant portions of the pretensioner pertaining to the first
embodiment;

[0049]FIG. 3 is an enlarged side sectional view of configuration of
relevant portions of the pretensioner pertaining to the first embodiment;

[0050]FIG. 4 is an enlarged plan sectional view of configurations of
relevant portions of the pretensioner pertaining to the first embodiment;

[0051]FIG. 5 is an enlarged plan sectional view corresponding to FIG. 4
showing a first modification of the first embodiment;

[0052]FIG. 6 is an enlarged plan sectional view corresponding to FIG. 4
showing a second modification of the first embodiment;

[0053]FIG. 7 is an enlarged plan sectional view corresponding to FIG. 4
showing a third modification of the first embodiment;

[0054]FIG. 8 is an enlarged exploded perspective view corresponding to
FIG. 2 showing a fourth modification of the first embodiment;

[0055]FIG. 9 is an enlarged plan sectional view corresponding to FIG. 4
showing the fourth modification of the first embodiment;

[0056] FIG. 10 is an enlarged exploded perspective view corresponding to
FIG. 2 showing a fifth modification of the first embodiment;

[0057]FIG. 11 is an enlarged plan sectional view corresponding to FIG. 4
showing a sixth modification of the first embodiment;

[0058]FIG. 12 is an enlarged plan sectional view corresponding to FIG. 4
showing a seventh modification of the first embodiment;

[0059]FIG. 13 is an enlarged exploded perspective view corresponding to
FIG. 2 showing an eighth modification of the first embodiment;

[0060]FIG. 14 is an enlarged exploded perspective view corresponding to
FIG. 2 showing a ninth modification of the first embodiment;

[0061]FIG. 15 is an enlarged side sectional view corresponding to FIG. 3
showing the ninth modification of the first embodiment;

[0062]FIG. 16 is an enlarged exploded perspective view corresponding to
FIG. 2 showing a tenth modification of the first embodiment;

[0063]FIG. 17 is an enlarged side sectional view corresponding to FIG. 3
showing an eleventh modification of the first embodiment;

[0064]FIG. 18 is an enlarged exploded perspective view corresponding to
FIG. 2 showing configurations of relevant portions of a pretensioner
pertaining to a second embodiment;

[0065]FIG. 19 is an enlarged side sectional view corresponding to FIG. 3
showing configurations of relevant portions of the pretensioner
pertaining to the second embodiment;

[0066] FIG. 20 is an enlarged side sectional view corresponding to FIG. 19
showing a first modification of the second embodiment;

[0067]FIG. 21 is an enlarged side sectional view corresponding to FIG. 19
showing a second modification of the second embodiment;

[0068]FIG. 22 is an enlarged exploded perspective view corresponding to
FIG. 2 showing configurations of relevant portions of a pretensioner
pertaining to a third embodiment;

[0069]FIG. 23 is an enlarged side sectional view corresponding to FIG. 3
showing configurations of relevant portions of the pretensioner
pertaining to the third embodiment;

[0070]FIG. 24 is an enlarged side sectional view corresponding to FIG. 23
showing a first modification of the third embodiment;

[0071]FIG. 25A and FIG. 25B are enlarged plan sectional views showing the
first modification of the third embodiment;

[0072]FIG. 26 is an enlarged exploded perspective view corresponding to
FIG. 2 showing configurations of relevant portions of a pretensioner
pertaining to a fourth embodiment;

[0073]FIG. 27 is an enlarged side sectional view corresponding to FIG. 3
showing configurations of relevant portions of the pretensioner
pertaining to the fourth embodiment;

[0074]FIG. 28 is an enlarged plan sectional view corresponding to FIG. 4
showing configurations of relevant portions of the pretensioner
pertaining to the fourth embodiment;

[0075]FIG. 29 is a perspective view of a plug serving as filter unit in
the fourth embodiment; and

[0076] FIG. 30 is an enlarged perspective view showing a state where the
plug is attached.

DETAILED DESCRIPTION OF THE INVENTION

[0077] Embodiments of exemplary examples of the present invention will be
described on the basis of FIG. 1 to FIG. 25. In describing the
embodiments below, in relation to portions that are basically identical
to those in preceding embodiments and modifications, identical reference
signs will be given thereto and detailed description thereof will be
omitted.

Configuration of First Embodiment

(Basic Configuration of Pretensioner 10)

[0078] In FIG. 1, a pretensioner 10 pertaining to a first embodiment is
shown by way of a side view. As shown in FIG. 1, the pretensioner 10 is
equipped with a cylinder 12 serving as a pretensioner body. The cylinder
12 is formed in a circular tube shape whose axial direction is tilted in
a vehicle width direction with respect to a vehicle up-and-down
direction. The cylinder 12 is placed on the outer side of a leg plate 18
configuring a frame 16 of a webbing retractor 14 and is fixed to the leg
plate 18 by a predetermined fixing bracket or the like.

[0079] A gas generator 20 serving as gas generating units is attached to
the axial direction upper end portion of the cylinder 12. The gas
generator 20 is electrically connected via an ECU serving as control unit
to a battery installed in the vehicle and an acceleration sensor that
detects the acceleration of the vehicle at the time of a vehicle impact.
When a detection signal from the acceleration sensor is inputted to the
ECU, the ECU actuates the gas generator 20. The gas generator 20 causes
an agent such as a gas-generating agent to combust and jets a gas toward
the inside of the cylinder 12 (the lower side of the cylinder 12).

[0080] A piston 22 serving as a spool driving member is disposed on the
inner side of the cylinder 12. The piston 22 is equipped with a
substantially circular cylinder-shaped piston body 24 serving as a
driving member body. The axial direction of the piston body 24 is the
same direction as the axial direction of the cylinder 12, and the outer
diameter dimension of the piston body 24 is set shorter than the inner
diameter dimension of the cylinder 12. An X-ring 26 serving as a sealing
member (an annular sealing member) that configures the piston 22 together
with the piston body 24 is attached to the piston body 24.

[0081] The X-ring 26 is formed in a ring-like shape overall. The
cross-sectional shape of the X-ring 26 when the X-ring 26 is cut along
its radial direction is a substantial X shape. The X-ring 26 is formed by
a synthetic resin material capable of elastic deformation such as rubber
and is attached to the outer peripheral portion of the piston body 24 in
a state where the X-ring 26 is elastically deformed and its diameter is
expanded. In this way, the inner peripheral portion of the X-ring 26 that
has been attached to the piston body 24 presses against the outer
peripheral portion of the piston body 24 to thereby seal the space
between the outer peripheral portion of the piston body 24 and the inner
peripheral portion of the X-ring 26, and the outer peripheral portion of
the X-ring 26 presses against the inner peripheral portion of the
cylinder 12 to thereby seal the space between the inner peripheral
portion of the cylinder 12 and the outer peripheral portion of the X-ring
26.

[0082] A flange portion 28 that configures the piston 22 together with the
piston body 24 and the X-ring 26 is formed on the axial direction lower
end portion of the piston body 24. The flange portion 28 is formed in a
disc shape whose outer diameter dimension is slightly shorter than the
inner diameter dimension of the cylinder 12. The flange portion 28 is
formed coaxially with respect to the piston body 24. In a state where the
piston 22 has been placed on the inner side of the cylinder 12, a slight
gap is formed between the inner peripheral portion of the cylinder 12 and
the outer peripheral portion of the flange portion 28.

[0083] A rack bar 30 is disposed on the side of the flange portion 28
opposite the piston body 24 side. The rack bar 30 is formed in a rod-like
shape whose cross-sectional shape is rectangular and whose lengthwise
direction is along the axial direction of the cylinder 12. The rack bar
30 is integrally connected to the flange portion 28 at the lengthwise
direction proximal end portion of the rack bar 30. Rack teeth 32 are
formed on one width direction end of the rack bar 30. The rack teeth 32
are formed every predetermined interval between the lengthwise direction
distal end of the rack bar 30 and the lengthwise direction middle portion
of the rack bar 30.

[0084] A pinion 34 is disposed under the cylinder 12. The pinion 34 is
supported, in such a way that it may freely rotate, on a rod-like shaft
portion 36. The axial direction proximal end portion of the shaft portion
36 is formed projecting coaxially from one axial direction end portion of
a spool 38 or one axial direction end portion of a torsion shaft that is
disposed coaxially with respect to the spool 38 and is connected in such
a way as to be incapable of relative rotation with respect to the spool
38.

[0085] A clutch member 40 is attached to the pinion 34. When the pinion 34
rotates in a retraction direction that is one direction about its central
axis, part of the clutch member 40 deforms and becomes substantially
integrally coupled to the spool 38. Because of this, the pinion 34
becomes coaxially and integrally coupled to the spool 38 via the deformed
clutch member 40. The lengthwise direction proximal end side of a long
band-like webbing 42 is fixed to the spool 38, and the webbing 42 is
retracted onto the spool 38 when the spool 38 rotates in the retraction
direction.

(Characteristic Configurations of Pretensioner 10)

[0086] A gas escape hole 52 is formed in the piston 22. The gas escape
hole 52 is equipped with an attachment hole 54. The attachment hole 43 is
formed as a circular hole whose depth direction is along the axial
direction of the piston 22. One end of the attachment hole 54 opens at
the end surface of the piston body 24 on the side opposite the flange
portion 28 side--that is, the end surface of the piston body 24 on the
gas generator 20 (gas generating units) side.

[0087] Further, a regulation hole 58 is formed continuously from the other
end of the attachment hole 54 and coaxially with respect to the
attachment hole 54. The regulation hole 58 is formed in the shape of a
circular truncated cone whose inner diameter dimension on one end is
equal to the inner diameter dimension of the attachment hole 54 and whose
inner diameter dimension gradually becomes smaller away from the
attachment hole 54 along the axial direction of the piston 22. A gas flow
rate adjusting hole 60 serving as a gas flow rate adjusting portion is
formed continuously from the other end of the regulation hole 58 (the end
portion of the regulation hole 58 on the side opposite the attachment
hole 54 side). The open shape of the gas flow rate adjusting hole 60 is
set on the basis of the flow rate of the gas to be passed through the gas
flow rate adjusting hole 60 per unit of time in a case where the internal
pressure inside the cylinder 12 between the gas generator 20 and the
piston 22 is a predetermined value. The end portion of the gas flow rate
adjusting hole 60 on the side opposite the regulation hole 58 side opens
at the end surface of the flange portion 28 on the side opposite the
piston body 24 side.

[0088] A filter member 62 serving as filter unit is press-fitted into the
attachment hole 54. The filter member 62 basically is formed in a
circular column shape. The outer diameter dimension of the filter member
62 is equal to the inner diameter dimension of the attachment hole 54,
and the axial direction dimension of the filter member 62 is equal to the
axial direction length of the attachment hole 54. Numerous vent holes 64
serving as vent portions are formed in the filter member 62. Each of the
vent holes 64 is formed as a cross-sectionally circular hole whose one
end opens at one axial direction end surface of the filter member 62 and
whose other end opens at the other axial direction end surface of the
filter member 62. The vent holes 64 basically open at only both of their
ends, but due to steps and forming methods of the filter member 62 and
the vent holes 64 in the filter member 62, vent holes that open at both
ends and also at the outer peripheral surface of the filter member 62 may
also exist.

[0089] The individual open shapes of the vent holes 64 are smaller than
the open shape of the gas flow rate adjusting hole 60. That is, in a case
where the open shapes of the vent holes 64 and the open shape of the gas
flow rate adjusting hole 60 are seen superimposed in a plan view, the
open shape of the gas flow rate adjusting hole 60 is larger than the open
shapes of the vent holes 64. Further, the setting range of the vent holes
64 in the end surfaces of the filter member 62 is larger than the open
shape of the gas flow rate adjusting hole 60. Consequently, when the open
shape of the gas flow rate adjusting hole 60 and the shape of the end
surface of the filter member 62 on the side opposite the gas flow rate
adjusting hole 60 side are seen superimposed, any of the plural vent
holes 64 are positioned outside the range of the gas flow rate adjusting
hole 60. For this reason, even if cinders 56 come into contact with the
axial direction one end surface of the filter member 62 and any of the
vent holes 64 become blocked by the cinders 56, any of the other vent
holes 64 do not become blocked by the cinders 56.

[0090] Moreover, the open area of each of the vent holes 64 and the number
of the vent holes 64 are set in such a way that the sum total of the open
areas of all of the vent holes 64 in the end surface of the filter member
62 becomes larger than the open area of the gas flow rate adjusting hole
60 on the flange portion 28 side.

[0091] In relation to the individual open shapes of the vent holes 64, for
example, if the shapes of the cinders 56 are predictabel, it is preferred
that the individual open shapes of the vent holes 64 be set smaller than
the smallest width dimension of the cinders 56 when the cinders 56 are
seen from various directions. Further, if the shapes of the cinders 56
are unclear, it is preferred that the individual open shapes of the vent
holes 64 be set smaller than the smallest width dimension of the agent
before combustion when the agent before combustion is seen from various
directions.

[0092] Further, the inner diameter dimension of the attachment hole 54
into which the filter member 62 is press-fitted is equal to the outer
diameter dimension of the filter member 62, but the regulation hole 58 is
formed in the shape of a circular truncated cone whose inner diameter
dimension becomes shorter away from the attachment hole 54. For this
reason, the filter member 62 that has been press-fitted into the
attachment hole 54 does not enter the regulation hole 58, and the open
ends of the vent holes 64 in the end surface of the filter member 62 on
the side that has been press-fitted into the attachment hole 54 do not
become blocked by the inner peripheral surface of the regulation hole 58
or the like.

[0093] <Action and Effects of First Embodiment>

(Basic Operation of Pretensioner 10)

[0094] When, in a state where the vehicle occupant seated in the vehicle
is wearing the webbing 42, a state of sudden deceleration that is similar
to a case where the vehicle impacts an obstacle in front of the vehicle
arises and the acceleration sensor detects the deceleration
(acceleration) of the vehicle at this time, the ECU actuates the gas
generator 20. When the gas generator 20 is actuated, the agent such as a
gas-generating agent inside the gas generator 20 is combusted, whereby
the gas is instantaneously generated. The gas that has been generated is
supplied to the inside of the cylinder 12.

[0095] Then, when the internal pressure inside the cylinder 12 between the
piston 22 and the gas generator 20 rises, the piston 22 descends and the
rack teeth 32 of the rack bar 30 integrated with the piston 22 mesh with
the pinion 34 and cause the pinion 34 to rotate in the retraction
direction. When the pinion 34 rotates in the retraction direction,
deformation arises in the clutch member 40 that is attached in such a way
as to be incapable of relative rotation with respect to the pinion 34,
and the clutch member 40 becomes integrally connected to the spool 38.
When the pinion 34 becomes coaxially and integrally connected to the
spool 38 via the clutch member 40 in this way, the rotation of the pinion
34 in the retraction direction is transmitted to the spool 38 and causes
the spool 38 to rotate in the retraction direction, and the webbing 42
worn on the body of the vehicle occupant is retracted onto the spool 38.
Because of this, the body of the vehicle occupant becomes restrained by
the webbing 42 more strongly than before.

(Characteristic Operation of the Pretensioner 10 and Effects Thereof)

[0096] In the pretensioner 10, the gas flow rate adjusting hole 60 formed
in the piston 22 is connected to the attachment hole 54 via the
regulation hole 58. The filter member 62 is press-fitted into the
attachment hole 54, but because the vent holes 64 open at both ends of
the filter member 62, the regulation hole 58 is connected to the vent
holes 64. Consequently, the upper side of the piston 22 (the gas
generator 20 side) inside the cylinder 12 and the lower side of the
piston 22 (the side opposite the gas generator 20 side) inside the
cylinder 12 are communicated with each other via the gas flow rate
adjusting hole 60, the regulation hole 58, and the vent holes 64 in the
filter member 62.

[0097] For this reason, after the sliding of the piston 22 resulting from
the rise in the internal pressure inside the cylinder 12 has ended, the
gas passes through the vent holes 64 in the filter member 62, the
regulation hole 58, and the gas flow rate adjusting hole 60 to the lower
side of the piston 22 inside the cylinder 12 and escapes from the open
end on the lower side of the cylinder 12. Because of this, when the
pretensioner 10 has been actuated, the internal pressure inside the
cylinder 12 on the upper side of the piston 22 is not maintained in a
high state.

[0098] Further, also when the piston 22 is sliding because of the rise in
the internal pressure inside the cylinder 12, the gas passes through the
vent holes 64 in the filter member 62, the regulation hole 58, and the
gas flow rate adjusting hole 60. The quantity of the gas that passes
through the vent holes 64 in the filter member 62, the regulation hole
58, and the gas flow rate adjusting hole 60 in this state is decided by
the inner diameter dimension of the gas flow rate adjusting hole 60 (the
inner peripheral shape of the gas flow rate adjusting hole 60). The inner
diameter dimension of the gas flow rate adjusting hole 60 (the inner
peripheral shape of the gas flow rate adjusting hole 60)--and therefore
the gas passage quantity--is set in such a way that there is no hindrance
with respect to the descent of the piston 22 and the rack bar 30 causing
the pinion 34 to rotate in the retraction direction. Consequently, the
gas escapes also when the piston 22 is sliding because of the rise in the
internal pressure inside the cylinder 22, but the piston 22 can be
sufficiently lowered and the pinion 34--and therefore the spool 38--can
be caused to rotate in the retraction direction.

[0099] When the gas generator 20 is actuated, the agent such as a
gas-generating agent is combusted, the gas is produced, and the cinders
56 of the agent are released into the inside of the cylinder 12 together
with the gas. Here, in the pretensioner 10, although the individual open
shapes of the vent holes 64 are set smaller than the open shape of the
gas flow rate adjusting hole 60, the setting range of the vent holes 64
in the end surface of the filter member 62 on the side opposite the gas
flow rate adjusting hole 60 side is larger than the open shape of the gas
flow rate adjusting hole 60. That is, when the open shape of the gas flow
rate adjusting hole 60 and the shape of the end surface of the filter
member 62 on the side opposite the gas flow rate adjusting hole 60 side
are superimposed, any of the plural vent holes 64 are positioned outside
the range of the gas flow rate adjusting hole 60.

[0100] For this reason, even if the cinders 56 come into contact with the
axial direction one end surface of the filter member 62 and any of the
vent holes 64 become blocked by the cinders 56, any of the other vent
holes 64 do not become blocked by the cinders 56.

[0101] Moreover, the open area of each of the vent holes 64 and the number
of the vent holes 64 are set in such a way that the sum total of the open
areas of all of the vent holes 64 in the end surface of the filter member
62 becomes larger than the open area of the gas flow rate adjusting hole
60 on the flange portion 28 side. For this reason, even if the cinders 56
come into contact with the axial direction one end surface of the filter
member 62 and any of the vent holes 64 become blocked by the cinders 56,
any of the other vent holes 64 do not become blocked by the cinders 56.
For this reason, even if the cinders 56 block any of the vent holes 64,
the difference between the sum total of the open areas of the vent holes
64 not blocked by the cinders 56 and the open area of the gas flow rate
adjusting hole 60 becomes smaller, but the gas with the necessary flow
rate can be released.

[0102] <Modifications of First Embodiment>

[0103] Next, modifications of the present embodiment will be described.

[0104] (First Modification)

[0105] As described above, in the present embodiment, the numerous vent
holes 64 are formed in the filter member 62. However, the vent portion
may also be single as long as the cinders 56 cannot pass through the vent
portion and the setting range of the vent portion is larger than the
cinders 56. That is, in a first modification of the present embodiment
shown in FIG. 5, a single curved slit-like vent hole 74 is formed in a
filter member 72 serving as filter unit. The lengthwise dimension of the
vent hole 74 in plan view is larger than the largest projected shape of
the cinders 56, and the width dimension of the vent hole 74 is a size
through which the cinders 56 cannot pass. Even with this configuration
equipped with the vent hole 74, the same action as in the first
embodiment can be provided and the same effects as in the first
embodiment can be obtained.

[0106] (Second Modification)

[0107] Further, in the present embodiment, the numerous vent holes 64 are
formed on the inner side of the outer peripheral portion of the filter
member 62. However, the pretensioner 10 may also be given a configuration
where a gap is formed between the inner peripheral portion of the
attachment hole and the outer peripheral portion of the filter unit
attached to the attachment hole, and the gap may be used as the vent
portion.

[0108] Namely, in a second modification of the present embodiment shown in
FIG. 6, a filter member 82 has a circular cylinder shape whose outer
diameter dimension is substantially equal to the inner diameter dimension
of the attachment hole 54, but plural grooves 84 serving as vent portions
are formed at the outer peripheral portion of the filter member 82 having
every predetermined interval in the circumferential direction of the
filter member 82. The grooves 84 open at both axial direction ends of the
filter member 82 and also open at the outer peripheral portion of the
filter member 82. Because the grooves 84 are formed, the filter member 82
does not strictly speaking have a circular cylinder shape, and gaps
serving as vent portions that open at both ends of the attachment hole 54
are formed between the grooves 84 and the inner peripheral portion of the
attachment hole 54. Even with this configuration, the same action as in
the first embodiment can be provided and the same effects as in the first
embodiment can be obtained.

[0109] (Third Modification)

[0110] Further, in a third modification of the present embodiment shown in
FIG. 7, the outer peripheral shape of a filter member 92 serving as
filter unit is formed in a polygonal shape (in this modification, a
hexagonal shape) that is inscribed in the inner peripheral shape of the
attachment hole 54. For this reason, when the filter member 92 is
press-fitted into the attachment hole 54, plural gaps 94 serving as vent
portions that open at both ends of the attachment hole 54 are formed
between the inner peripheral portion of the attachment hole 54 and the
outer peripheral portion of the filter member 92. Even with this
configuration, the same action as in the first embodiment can be provided
and the same effects as in the first embodiment can be obtained.

[0111] (Fourth Modification)

[0112] Moreover, in a fourth modification of the present embodiment shown
in FIG. 8 and FIG. 9, a filter member 102 is formed by bending a
cross-sectionally circular rod-like member into a substantial V shape.
The filter member 102 is press-fitted from its bent portion side into an
attachment hole 103 instead of the attachment hole 54. The attachment
hole 103 differs from the attachment hole 54 in that the attachment hole
103 is formed in a long hole shape (or an elliptical shape) whose open
width dimension is smaller than the sum of the diameter dimension of the
gas flow rate adjusting hole 60 and the outer diameter dimension of the
filter member 102. For this reason, plural gaps 104 serving as vent
portions that open at both ends of the attachment hole 103 are formed
between the outer peripheral portion of the filter member 102
press-fitted into the attachment hole 103 and the inner peripheral
portion of the attachment hole 103. Even with this configuration, the
same action as in the first embodiment can be provided and the same
effects as in the first embodiment can be obtained.

[0113] (Fifth Modification)

[0114] Further, in a fifth modification of the present embodiment shown in
FIG. 10, a filter member 112 serving as filter unit is formed as a result
of a plate material whose width dimension is about the same as the depth
dimension of the attachment hole 54 being bent into a substantial V shape
about an axis that takes the width direction as its axial direction. In a
state where the filter member 112 has been press-fitted into the
attachment hole 54, both lengthwise direction ends of the filter member
112 and the bent portion of the filter member 112 press against the inner
peripheral portion of the attachment hole 54. For this reason, plural
gaps serving as vent portions that open at both ends of the attachment
hole 54 are formed between the outer peripheral portion of the filter
member 112 press-fitted into the attachment hole 54 and the inner
peripheral portion of the attachment hole 54. Even with this
configuration, the same action as in the first embodiment can be provided
and the same effects as in the first embodiment can be obtained.

[0115] (Sixth Modification)

[0116] Moreover, in a sixth modification of the present embodiment shown
in FIG. 11, the gas escape hole 52 is formed at an attachment hole 122
instead of the attachment hole 54. The attachment hole 122 differs from
the attachment hole 54 in that the open shape of the attachment hole 122
is formed in an elliptical shape. A filter member 124 serving as filter
unit is formed in a circular column shape whose outer diameter dimension
is substantially equal to the minor diameter dimension of the attachment
hole 122. When the filter member 124 is press-fitted into the attachment
hole 122, two gaps 126 serving as vent portions are formed on both sides
of the filter member 124 in the major diameter direction of the
attachment hole 122. Even with this configuration, the same action as in
the first embodiment can be provided and the same effects as in the first
embodiment can be obtained.

[0117] (Seventh Modification)

[0118] Moreover, in a seventh modification of the present embodiment shown
in FIG. 12, the gas escape hole 52 is formed at an attachment hole 132
instead of the attachment hole 54. The attachment hole 132 differs from
the attachment hole 54 in that the open shape of the attachment hole 132
is formed in a polygonal shape (in this modification, a hexagonal shape).
A filter member 124 serving as filter unit is set to a length where the
outer diameter dimension of the filter member 124 is capable of being
inscribed in the attachment hole 132. When the filter member 124 is
press-fitted into the attachment hole 132, plural gaps 136 serving as
vent portions are formed between the inner peripheral portion of the
attachment hole 132 and the outer peripheral portion of the filter member
124. Even with this configuration, the same action as in the first
embodiment can be provided and the same effects as in the first
embodiment can be obtained.

[0119] (Eighth Modification)

[0120] Moreover, in an eighth modification of the present embodiment shown
in FIG. 13, the pretensioner 10 is equipped with a filter member 142
serving as filter unit. The filter member 142 is equipped with a circular
cylinder portion 144. The outer diameter dimension of the circular
cylinder portion 144 is set sufficiently smaller than the inner diameter
dimension of the attachment hole 54. On the upper side of the axial
direction middle portion of the circular cylinder portion 144, a pair of
pressing portions 146 project outward in the radial direction of the
circular cylinder portion 144 from the outer peripheral portion of the
circular cylinder portion 144. The pressing portions 146 are formed in
such a way as to oppose each other with respect to the circular cylinder
portion 144. The distance from the distal end of one of the pressing
portions 146 to the distal end of the other of the pressing portions 146
along the radial direction of the circular cylinder portion 144 is
substantially equal to the inner diameter dimension of the attachment
hole 54.

[0121] For this reason, when the filter member 142 is attached to the
attachment hole 54, the distal ends of both of the pressing portions 146
press against the inner peripheral portion of the attachment hole 54.
Moreover, in this state, gaps serving as vent portions are formed between
the circular cylinder portion 144 and the inner peripheral portion of the
attachment hole 54. Even with this configuration, the same action as in
the first embodiment can be provided and the same effects as in the first
embodiment can be obtained.

[0122] (Ninth Modification)

[0123] Further, in the present embodiment, the filter member 62 serving as
filter unit is formed in a circular column shape, but the configuration
(shape) of the filter unit is not limited to such a shape. That is, in a
ninth modification of the present embodiment shown in FIG. 14 and FIG.
15, a filter member 152 serving as filter unit is formed in a bottomed
circular tube shape, with one end thereof being open. Additionally,
numerous vent holes 156 serving as vent portions are formed in a bottom
portion 154. The filter member 152 is press-fitted from its open end side
into the attachment hole 54. Even with this configuration, the same
action as in the first embodiment can be provided and the same effects as
in the first embodiment can be obtained.

[0124] Moreover, because the filter member 152 has a circular tube shape,
the bottom portion 154 is spaced apart from the bottom of the attachment
hole 54 in a state where the filter member 152 has been press-fitted from
its open end side into the attachment hole 54. For this reason, even if
the regulation hole 58 is not disposed between the attachment hole 54 and
the gas flow rate adjusting hole 60, the vent holes 156 formed in the
bottom portion 154 do not become blocked by the bottom of the attachment
hole 54.

[0125] (Tenth Modification)

[0126] Further, in the present embodiment, the pretensioner 10 has a
configuration where the filter member 62 serving as filter unit is fixed
to the piston 22 by press-fitting the filter member 62 into the
attachment hole 54, but the structure for fixing the filter unit is not
limited to this configuration.

[0127] That is, in a tenth modification of the present embodiment shown in
FIG. 10, a filter member 162 serving as filter unit is equipped with a
disc-shaped filter portion 164 whose outer peripheral shape is larger
than the inner peripheral shape of the attachment hole 54. Numerous vent
holes 166 serving as vent portions are penetratingly formed in the filter
portion 164. A tabular fixing piece 168 extends from part of the outer
periphery of the filter portion 164. The fixing piece 168 is bent at its
extension direction middle portion into a substantial V shape.

[0128] A fixing hole 170 is formed in the piston body 24 in correspondence
to the fixing piece 168. The fixing hole 170 is formed in a rectangular
shape whose length dimension is substantially equal to the width
dimension of the fixing piece 168 and whose width dimension is slightly
larger than twice the thickness dimension of the fixing piece 168. When
the fixing piece 168 is inserted into the fixing hole 170 until the
filter portion 164 comes into contact with the end surface of the piston
body 24, the filter member 162 becomes fixed to the piston 22 because of
the elasticity of the fixing piece 168. Even with this configuration, the
same action as in the first embodiment can be provided and the same
effects as in the first embodiment can be obtained.

[0129] (Eleventh Modification)

[0130] Further, in an eleventh modification of the present embodiment
shown in FIG. 17, a filter member 192 serving as filter unit is formed in
a bottomed circular tube shape that opens toward the piston 22 side.
Numerous vent holes 194 serving as vent portions are formed in a bottom
portion 193 of the filter member 192. A female screw 195 is formed on the
inner peripheral portion of the filter member 192. When the female screw
195 is screwed onto a male screw 196 formed on the outer peripheral
portion of the piston body 24, the filter member 192 becomes fixed to the
piston 22 in a state where the bottom portion 193 is spaced apart from
the end surface of the piston body 24. Even with this configuration, the
same action as in the first embodiment can be provided and the same
effects as in the first embodiment can be obtained.

[0131] It goes without saying that, in each of the above modifications,
the formation conditions (open shape and formation range) of the
configurations corresponding to the vent portions such as the vent holes
74 and 156, the grooves 84, and the gaps 94, 104, 126, and 136 follow the
formation conditions (open shape and formation range) of the vent holes
74 in the first embodiment.

Configuration of Second Embodiment

[0132] Next, a second embodiment will be described.

[0133] In FIG. 18, configurations of relevant portions of a pretensioner
200 pertaining to the second embodiment are shown by way of an exploded
perspective view corresponding to FIG. 2 that described the first
embodiment. As shown in FIG. 18, the pretensioner 200 is equipped with a
filter member 202 serving as filter unit. The filter member 202 is
equipped with a disc-shaped portion 204. The disc portion 204 is formed
in such a way that its outer diameter dimension is even larger than the
larger of the inner diameter dimension of the attachment hole 54 and the
maximum length of the maximum projected shape of the cinders 56 and is
equal to or less than the outer diameter dimension of the piston body 24.

[0134] One or plural projections 206 are formed on one thickness direction
surface of the disc portion 204. As shown in FIG. 19, when the disc
portion 204 is placed on the end surface of the piston body 24 in such a
way that the projections 206 come into contact with the end surface of
the piston body 24, a gap 208 serving as a vent portion is formed between
the disc portion 204 and the end surface of the piston body 24. In a case
where the open shape of the gap 208 and the cross-sectional shape of the
gas flow rate adjusting hole 60 are seen superimposed in a plan view, the
open shape of the gap 208 and the cross-sectional shape of the gas flow
rate adjusting hole 60 do not coincide with each other. Moreover, because
the outer peripheral shape of the disc portion 204 is larger than the
cross-sectional shape of the gas flow rate adjusting hole 60, the setting
range of the gap 208 becomes larger than the setting range of the gas
flow rate adjusting hole 60.

[0135] Moreover, a pair of holding pieces 210 are formed on parts of the
outer periphery of the disc portion 204. The holding pieces 210 are
formed in such a way that one opposes the other via the disc portion 204.
The holding pieces 210 extend toward the lower side of the cylinder 12
and are bent or curved at their extension direction middle portions in a
substantial V shape inward in the radial direction of the disc portion
204. The interval between the bent portion of one of the holding pieces
210 and the bent portion of the other of the holding pieces 210 is set
shorter than the outer diameter dimension of the piston body 24. In a
state where the disc portion 204 has been placed on the end surface of
the piston body 24 in such a way that the projections 206 come into
contact with the end surface of the piston body 24, both of the holding
pieces 210 elastically hold the outer peripheral portion of the piston
body 24 on the upper side of the X-ring 26. Because of this, the filter
member 202 is fixed to the piston 22.

[0136] <Action and Effects of Second Embodiment>

[0137] In the present embodiment, a vent hole that penetrates the disc
portion 204 is not formed, so the gas that has been supplied to the
inside of the cylinder 12 passes between the outer peripheral portion of
the disc portion 204 and the outer peripheral portion of the piston body
24, flows in between the disc portion 204 and the end surface of the
piston body 24, passes through the gas escape hole 52, and flows out to
the lower side of the piston 22 and therefore the outer side of the
cylinder 12.

[0138] Here, the open shape of the gap 208 and the cross-sectional shape
of the gas flow rate adjusting hole 60 do not coincide with each other in
a plan view. Moreover, as described above, the setting range of the gap
208 is larger than the setting range of the gas flow rate adjusting hole
60, so no matter which part of the gap 208 the cinders 56 catch on, there
is a gap portion on which the cinders 56 do not catch. The difference
between the open area of the gap 208 and the cross-sectional area of the
gas flow rate adjusting hole 60 becomes smaller, but the gas with the
flow rate decided by the cross-sectional area of the gas flow rate
adjusting hole 60 can be released.

[0139] (First Modification)

[0140] In the present embodiment, the pretensioner 200 has a configuration
where the disc portion 204 is spaced apart from the end surface of the
piston body 24 and the filter member 202 is fixed to the piston 22 as a
result of the pair of holding pieces 210 holding the outer peripheral
portion of the piston body 24 in a state where the projections 206 have
been brought into contact with the end surface of the piston body 24.
However, the configuration by which the filter unit is fixed to the
piston 22 in a state where the filter unit is spaced apart from the end
surface of the piston body 24 is not limited to this configuration.

[0141] That is, in a first modification of the present embodiment shown in
FIG. 20, a circular cylinder-shaped boss 224 is formed coaxially with the
disc portion 204 from the center of the end surface, on the piston body
24 side, of the disc portion 204 of a filter member 222 serving as filter
unit. The height of the boss 224 (the axial direction length of the boss
224) is set to be same as the projecting dimension of the projections 206
as described above. A male screw 226 is formed coaxially with respect to
the boss 224 from the end surface of the boss 224 on the piston body 24
side. A female screw 228 that opens at the end surface of the piston body
24 is formed on the central axis of the piston body 24 in correspondence
to the male screw 226.

[0142] When the male screw 226 is screwed into the female screw 228 until
the end portion of the boss 224 on the piston body 24 side comes into
contact with the end surface of the piston body 24, the filter member 222
becomes fixed to the piston 22 in a state where the disc portion 204 is
spaced apart from the end surface of the piston body 24. Moreover,
because the axial direction length of the boss 224 is set to be the same
as the projecting dimension of the projections 206, the interval of the
gap (vent portion) between the disc portion 204 and the piston body 24 in
a state where the filter member 222 has been fixed to the piston 22
becomes the same as that of the gap 208 in the second embodiment.

[0143] Consequently, even with this configuration, the same action as in
the second embodiment can be provided and the same effects as in the
second embodiment can be obtained. Further, in this modification,
numerous vent holes 230 are penetratingly formed in the disc portion 204.
The vent holes 230 are set like the vent holes 64 formed in the filter
member 62 in the first embodiment, so in this modification also, the same
action as in the first embodiment can be provided and the same effects as
in the first embodiment can be obtained.

[0144] (Second Modification)

[0145] Further, in a second modification of the present embodiment shown
in FIG. 21, instead of the male screw 226, a coil spring 246 whose axial
direction is along the axial direction of the boss 224 is disposed on the
end portion of the boss 224 on the piston body 24 side. And instead of
the female screw 228, a circular hole 248 that opens at the end surface
of the piston body 24 is formed coaxially with respect to the piston body
24 on the central axis of the piston body 24. When the coil spring 246 is
press-fitted into the circular hole 248 counter to the elasticity of the
coil spring 246 until the end portion of the boss 224 on the piston body
24 side comes into contact with the end surface of the piston body 24,
the filter member 222 becomes fixed to the piston 22 in a state where the
disc portion 204 is spaced apart from the end surface of the piston body
24. Consequently, even with this configuration, the same action as in the
first modification of the present embodiment can be provided and the same
effects as in the first modification of the embodiment can be obtained.

Configuration of Third Embodiment

[0146] Next, a third embodiment will be described.

[0147] In FIG. 22, configurations of relevant portions of a pretensioner
260 pertaining to the third embodiment are shown by way of an exploded
perspective view corresponding to FIG. 2 that described the first
embodiment. As shown in FIG. 22, the pretensioner 260 is equipped with a
piston 262 serving as a spool driving member instead of the piston 22.
The piston 262 is equipped with a piston body 264 that configures a
filter member. The piston body 264 has a shape where grooves 266 serving
as vent portions that open at both axial direction ends of the piston
body 264 are formed every predetermined interval in the circumferential
direction of a circular cylinder shape like the piston body 24. In other
word, the grooves 266 are formed at the outer peripheral portion of the
piston body 264.

[0148] Further, an annular groove 268 is formed in the surface of a flange
portion 280 on the piston body 264 side. The annular groove 268 has a
ring-like shape along the outer peripheral portion of the piston body
264. All of the grooves 266 are communicated, at their end portions on
the flange portion 280 side, with the annular groove 268. Further, a gas
flow rate adjusting groove 270 serving as a gas flow rate adjusting
portion is formed in the surface of the flange portion 280 on the piston
body 264 side. The gas flow rate adjusting groove 270 is formed in such a
way that its lengthwise direction is along the radial direction of the
flange portion 280. One end of the gas flow rate adjusting groove 270 is
communicated with the annular groove 268, and the other end of the gas
flow rate adjusting groove 270 opens at the outer peripheral portion o
the flange portion 280. The area of the cross section of the gas flow
rate adjusting groove 270 when the gas flow rate adjusting groove 270 is
cut in a direction orthogonal to its lengthwise direction is set on the
basis of the flow rate of the gas to be passed through the gas flow rate
adjusting groove 270 per unit of time in a case where the internal
pressure inside the cylinder 12 between the gas generator 20 and the
piston 262 is a predetermined value.

[0149] Here, the shape of the gas flow rate adjusting groove 270 that
opens at part of the outer peripheral portion of the flange portion 280
(the open shape at the outer peripheral portion of the flange portion
280) and the open shapes of the grooves 266 are set in such a way that
they are offset from and do not coincide with each other in a plan view.
Moreover, the range of the open shape of the gas flow rate adjusting
groove 270 is narrower than the setting range of the grooves 266 along
the outer peripheral portion of the piston body 264, and the open area of
the gas flow rate adjusting groove 270 is smaller than the sum total of
the open areas of all of the grooves 266 on the piston body 264 end
surface side.

[0150] Further, a sleeve 272 serving an annular member that configures
filter unit together with the piston body 264 is attached to the piston
262. The sleeve 272 is equipped with a tubular portion 274. The tubular
portion 274 is formed in a circular tube shape whose inner diameter
dimension is equal to the outer diameter dimension of the circular
cylinder-shaped piston body 264 in a case where the grooves 266 are not
formed in the piston body 264. An outer diameter dimension of the tubular
portion 274 is shorter than the inner diameter dimension of the cylinder
12, and whose axial direction is along the axial direction of the
cylinder 12. A flange portion 276 projects outward in the radial
direction of the tubular portion 274 from the axial direction lower end
portion of the tubular portion 274.

[0151] The outer diameter dimension of the flange portion 276 is shorter
than the inner diameter dimension of the cylinder 12 and, particularly in
the present embodiment, is substantially equal to the outer diameter
dimension of the flange portion 280 of the piston 262. As shown in FIG.
23, the sleeve 272 is attached to the piston 262 by inserting the piston
body 264 into the inner side of the tubular portion 274 so that the end
surface of the flange portion 276 is brought into contact with the flange
portion 280. The openings of the grooves 266 on the piston body 264 outer
peripheral portion side become closed by the tubular portion 274, and the
opening of the annular groove 268 and the opening of the gas flow rate
adjusting groove 270 on the flange portion 280 end surface side become
closed by the flange portion 276.

[0152] <Action and Effects of Third Embodiment>

[0153] According to the pretensioner 260, the gas that has been generated
by the gas generator 20 passes through the grooves 266 formed in the
outer peripheral portion of the piston body 264 and reaches the annular
groove 268. The gas passes through the inside of the annular groove 268,
reaches the gas flow rate adjusting groove 270, passes through the gas
flow rate adjusting groove 270, escapes to the outer side of the flange
portion 280, passes between the outer peripheral portion of the flange
portion 280 and the inner peripheral portion of the cylinder 12, and is
released to the lower side of the piston 262. In this way, although the
gas passage path differs, in the present embodiment also the gas can
escape like in the first embodiment, so after the pretensioner 260 has
been actuated, the internal pressure inside the cylinder 12 on the upper
side of the piston 262 is not maintained in a high state.

[0154] Further, also when the piston 262 is sliding because of the rise in
the internal pressure inside the cylinder 12, the gas passes and escapes
through the grooves 266, the annular groove 268, and the gas flow rate
adjusting groove 270. However, the quantity of the gas that passes
through the grooves 266, the annular groove 268, and the gas flow rate
adjusting groove 270 in this state is decided by the cross-sectional area
of the gas flow rate adjusting groove 270, and the cross-sectional area
of the gas flow rate adjusting groove 270--and therefore the gas passage
quantity--is set in such a way that there is no hindrance with respect to
the descent of the piston 262 and the rack bar 30 causing the pinion 34
to rotate in the retraction direction. Consequently, the gas escapes also
when the piston 262 is sliding because of the rise in the internal
pressure inside the cylinder 22, but the piston 262 can be sufficiently
lowered and the pinion 34--and therefore the spool 38--can be caused to
rotate in the retraction direction.

[0155] Moreover, the open shapes of the grooves 266 and the open shape of
the gas flow rate adjusting groove 270 are set in such a way that the
shape of the gas flow rate adjusting groove 270 that opens at part of the
outer peripheral portion of the flange portion 280 (the open shape at the
outer peripheral portion of the flange portion 280) and the open shapes
of the grooves 266 are offset from and do not coincide with each other.
The range of the open shape of the gas flow rate adjusting groove 270 is
narrower than the setting range of the grooves 266 along the outer
peripheral portion of the piston body 264. For this reason, even if any
of the grooves 266 become blocked by the cinders 56, the other grooves
266 are open, so the gas can flow through the grooves 266 not blocked by
the cinders 256.

[0156] Moreover, the sum total of the open areas of the grooves 266 at the
end surface of the piston body 264 is larger than the cross-sectional
area of the gas flow rate adjusting groove 270, so even if any of the
grooves 266 becomes blocked by the cinders 56, the difference between the
sum total of the open areas of the other grooves 266 and the
cross-sectional area of the gas flow rate adjusting groove 270 becomes
smaller, but a sufficient gas passage quantity corresponding to the size
of the cross-sectional area of the gas flow rate adjusting groove 270 can
be ensured.

[0157] (First Modification)

[0158] In the present embodiment, the pretensioner 260 has a configuration
where the plural grooves 266 are formed in the outer peripheral portion
of the piston body 264, but the number of the grooves 266 formed in the
outer peripheral portion of the piston body 264 is in no way limited.
Further, in the present embodiment, the grooves 266 have a configuration
where they are communicated with the outer side of the outer peripheral
portion of the flange portion 280 via the annular groove 268 and the gas
flow rate adjusting groove 270 and where they are communicated with the
lower side of the piston 262 via the space between the outer peripheral
portion of the flange portion 280 and the inner peripheral portion of the
cylinder 12, but it suffices for the grooves 266 to eventually be
communicated with the lower side of the piston 262, and the gas passage
path is in no way limited. Moreover, in the present embodiment, the
sleeve 272 is used as the annular member. However, the configuration of
the annular member is not limited to the sleeve 272.

[0159] That is, according to a first modification of the present
embodiment shown in FIG. 24, FIG. 25A, and FIG. 25B, a single groove 266
is formed in the outer peripheral portion of the piston body 264.
Further, in this first modification, the annular groove 268 and the gas
flow rate adjusting groove 270 are not formed; instead, a gas flow rate
adjusting hole 292 serving as a gas flow rate adjusting portion is
formed. The gas flow rate adjusting hole 292 is formed as a through hole
whose one end opens, on the side of the piston body 264, at the end
surface of the flange portion 280 on the piston body 264 side and whose
other end opens at the end surface of the flange portion 280 on the side
opposite the piston body 264 side. The cross-sectional shape of the gas
flow rate adjusting hole 292 is circular, and as for the cross-sectional
area, the open shape is, like the gas flow rate adjusting hole 60 in the
first embodiment, set on the basis of the flow rate of the gas to be
passed through the gas flow rate adjusting hole 292 per unit of time in a
case where the internal pressure inside the cylinder 12 between the gas
generator 20 and the piston 262 is a predetermined value.

[0160] As shown in FIG. 25A and FIG. 25B, the groove 266 in the present
modification has a configuration where it curves in a larger radius of
curvature than the radial dimension of the gas flow rate adjusting hole
292 taking the central axis of the gas flow rate adjusting hole 292 as
the center of curvature. The shape of the groove 266 is not limited to
this shape. Moreover, a gas passage path resulting from the groove 266
and the gas flow rate adjusting hole 292 is configured by attaching to
the piston body 264 an X-ring 294 serving as an annular member whose
configuration is basically the same as that of the X-ring 26 heretofore
described.

Configuration of Fourth Embodiment

[0161] Next, a fourth embodiment will be described.

[0162] In FIG. 26, an exploded perspective view in which relevant portions
of a pretensioner 310 pertaining to the present embodiment are enlarged
is shown. In FIG. 27, a side sectional view in which relevant portions of
the pretensioner 310 are enlarged is shown. Moreover, in FIG. 28, a plan
sectional view in which relevant portions of the pretensioner 310 are
enlarged is shown. The one-dot chain line circle B in FIG. 28 is an
enlarged view of the inside of the one-dot chain line circle A in FIG. 8.

[0163] As shown in FIG. 26, FIG. 27, and FIG. 28, a plug 312 serving as a
filter unit is attached from the attachment hole 54 side to the gas
escape hole 52 formed in the piston 22 of the pretensioner 310. As shown
in FIG. 26 and FIG. 29, the plug 312 is equipped with an insertion
portion 314. The insertion portion 314 is equipped with an insertion
portion body 316. The outer peripheral shape of the insertion portion
body 316 is formed in a rectangle that is one form of a polygon and
particularly in the present embodiment, a square. The outer peripheral
shape of the insertion portion body 316 differs from the inner peripheral
shape of the attachment hole 54 that is formed in a circle.

[0164] As shown in FIG. 28, the length of the diagonal lines in the
cross-sectional shape of the insertion portion body 316 is set equal to
(strictly speaking, slightly smaller than) the diameter dimension of the
inner peripheral portion of the attachment hole 54. In a state where the
insertion portion body 316 has been inserted into the inner side of the
attachment hole 54, the corner portions (four corners) of the outer
peripheral portion of the insertion portion body 316 come into contact
with the inner peripheral portion of the attachment hole 54, and the
outer peripheral surface of the insertion portion body 316 excluding the
corner portions are positioned further on the inner side of the inner
peripheral portion of the attachment hole 54. For this reason, between
the inner peripheral surface of the attachment hole 54 and the outer
peripheral surface of the insertion portion body 316 excluding the corner
portions, gaps 318 serving as vent portions such as shown in FIG. 27 and
FIG. 28 are formed along the penetration direction of the attachment hole
54. That is, in the present embodiment, it can also be said that the
insertion portion body 316 of the plug 312 substantially configures the
filter unit.

[0165] The maximum open width of the gaps 318--that is, the interval
between the inner peripheral portion of the attachment hole 54 and the
outer peripheral portion of the insertion portion body 316 at the
portions where the inner peripheral portion of the attachment hole 54 and
the outer peripheral portion of the insertion portion body 316 are
furthest apart from each other--is from 0.1 mm to 0.3 mm, and is
specifically set about 0.2 mm. The gaps 318 whose open width is set to
this size have a lengthwise direction dimension that is set larger than
the diameter dimension of the inner peripheral portion of the gas flow
rate adjusting hole 60 and have a maximum width dimension (the
above-described maximum open width dimension) that is set smaller than
the diameter dimension of the inner peripheral portion of the gas flow
rate adjusting hole 60. For this reason, when the open shapes of the
individual gaps 318 and the open shape of the gas flow rate adjusting
hole 60 are seen superimposed in a plan view, the open shape of the gas
flow rate adjusting hole 60 does not coincide with the open shapes of the
gaps 318. Further, the sum total of the open areas of all of the gaps 318
becomes larger than the open area of the gas flow rate adjusting hole 60.

[0166] As shown in FIG. 26 and FIG. 29, a tapered portion 320 is formed
continuously from one lengthwise direction end of the insertion portion
body 316. The end portion of the tapered portion 320 on the insertion
portion body 316 side has the same shape as the cross-sectional shape of
the insertion portion body 316. However, the outer peripheral shape of
the tapered portion 320 gradually becomes smaller toward the side
opposite the insertion portion body 316 side so as to have a tapered
shape. A small diameter portion 322 is formed continuously from the end
portion of the tapered portion 320 on the side opposite the insertion
portion body 316 side. The length from the one end of the small diameter
portion 322 (the end portion of the small diameter portion 322 on the
side opposite the tapered portion 320 side) to the end of the insertion
portion body 316 (the end portion of the insertion portion body 316 on
the side opposite the tapered portion 320 side) is equal to or less than
the depth dimension of the attachment hole 54 in the gas escape hole 52.

[0167] Further, the length of the diagonal lines in the cross section of
the small diameter portion 322 is shorter than the diameter dimension of
the inner peripheral portion of the attachment hole 54. For this reason,
in a state where the insertion portion body 316 has been inserted into
the inside of the attachment hole 54, the corner portions (four corners)
of the small diameter portion 322 are spaced apart from the inner
peripheral portion of the attachment hole 54. In the present embodiment,
the tapered portion 320 and the small diameter portion 322 have similar
shapes with respect to the insertion portion body 316, but it is alright
if the outer peripheral shapes (cross-sectional shapes) of the tapered
portion 320 and the small diameter portion 322 do not have similar shapes
with respect to the outer peripheral shape (cross-sectional shape) of the
insertion portion body 316. It suffices as long as the tapered portion
320 has a tapered shape that becomes slenderer away from the insertion
portion body 316. Further, it suffices as long as the small diameter
portion 322 has a shape whose outer peripheral shape is smaller than that
of the insertion portion body 316 and where the entire outer peripheral
portion of the small diameter portion 322 is spaced apart from the inner
peripheral portion of the attachment hole 54 in a state where the
insertion portion body 316 has been inserted into the attachment hole 54.

[0168] As shown in FIG. 26 and FIG. 29, a head portion 332 serving as a
filter unit is formed on the side of the insertion portion body 316
opposite the tapered portion 320 side. The head portion 332 is formed in
a disc shape whose outer diameter dimension is larger than the inner
diameter dimension of the attachment hole 54 and a circular cylinder
shape whose axial direction dimension is relatively short. The head
portion 332 is concentric with the insertion portion body 316. As shown
in FIG. 27 and FIG. 30, in a state where the insertion portion body 316
has been inserted into the attachment hole 54, the head portion 332
coaxially covers the attachment hole 54, and the open end of the
attachment hole 54 in the piston body 24 is entirely hidden under the
head portion 332.

[0169] In this way, the head portion 332 cannot be inserted into the
attachment hole 54, so when the insertion portion body 316 is inserted
into the attachment hole 54, the head portion 332 comes into contact with
the end surface of the piston body 24 in the range of the open end of the
attachment hole 54. For that reason, the insertion portion body 316 does
not become inserted too much into the attachment hole 54 (that is, the
head portion 332 has the function of a stopper when inserting the
insertion portion body 316 into the attachment hole 54).

[0170] In the present embodiment, the outer peripheral shape of the head
portion 332 is circular, but it is alright if the outer peripheral shape
of the head portion 332 is not circular as long as the outer peripheral
shape of the head portion 332 is larger than the inner peripheral shape
of the attachment hole 54 and the open end of the attachment hole 54 is
entirely hidden under the head portion 332 in a state where the insertion
portion body 316 has been inserted into the attachment hole 54.

[0171] Further, as shown in FIG. 26 and FIG. 29, a peripheral wall 334 is
formed on the head portion 332. The peripheral wall 334 is formed in an
annular shape whose outer diameter dimension is equal to the outer
diameter dimension of the head portion 332, and the peripheral wall 334
is formed coaxially with respect to the head portion 332 from the end
surface of the head portion 332 on the insertion portion body 316 side.
The inner diameter dimension of the peripheral wall 334 is longer than
the length of the diagonal lines of the cross section of the insertion
portion body 316. For this reason, as shown in FIG. 29, an annular
communicative portion 336 continuing in the inner peripheral direction of
the peripheral wall 334 is formed between the inner peripheral portion of
the peripheral wall 334 and the outer peripheral portion of the insertion
portion body 316. Further, plural cutout portions 338 are formed in the
peripheral wall 334. The cutout portions 338 open at the end portion of
the peripheral wall 334 on the side opposite the head portion 332 side
and also open at the inner peripheral surface and the outer peripheral
surface of the peripheral wall 334. The open dimension of each of the
cutout portions 338 along the circumferential direction of the head
portion 332 in the outer peripheral surface of the peripheral wall 334 is
set to about 1.4 mm, and the open dimension of each of the cutout
portions 338 along the axial direction of the head portion 332 is set to
about 0.4 mm.

[0172] The cutout portions 338 are formed in such a way as to oppose the
sides of the rectangle that is the cross-sectional shape of the insertion
portion body 316. The cutout portions 338 lead to the gaps 318 between
the outer peripheral portion of the insertion portion body 316 and the
inner peripheral portion of the attachment hole 54 via the annular
communicative portion 336 and further lead to the gas flow rate adjusting
hole 60 via the gaps 318.

[0173] For this reason, even when the head portion 332 comes into contact
with the end surface of the piston body 24 in the range of the open end
of the attachment hole 54 as a result of the insertion portion body 316
being inserted into the attachment hole 54, the gaps 318 and the portion
of the piston body 24 on the side opposite the rack bar 30 side in the
space on the inner side of the cylinder 12 become communicated with each
other via the cutout portions 338 that open at the outer peripheral
surface of the peripheral wall 334 and the annular communicative portion
336.

[0174] In the present embodiment, the diameter dimension of the inner
peripheral portion of the gas flow rate adjusting hole 60 is set to about
0.5 mm and specifically from 0.4 mm to 0.6 mm.

[0175] That is, in the present embodiment, the open dimension of each of
the cutout portions 338 along the circumferential direction of the head
portion 332 is set larger than the diameter dimension of the inner
peripheral portion of the gas flow rate adjusting hole 60, and the open
dimension of each of the cutout portions 338 along the axial direction of
the head portion 332 is set smaller than the diameter dimension of the
inner peripheral portion of the gas flow rate adjusting hole 60.
Moreover, when the open shapes of the individual cutout portions 338 and
the open shape of the gas flow rate adjusting hole 60 are seen
superimposed, they are offset from and do not coincide with each other in
a plan view. Further, the sum total of the open areas of all of the
cutout portions 338 on the outer peripheral surface side of the
peripheral wall 334 is larger than the open area of the gas flow rate
adjusting hole 60.

[0176] In relation to the individual open shapes of the cutout portions
338, for example, if the shapes of the cinders 56 are already known, it
is preferred that the individual open shapes of the cutout portions 338
be set smaller than the smallest width dimension of the cinders 56 when
the cinders 56 are seen from various directions. Further, if the shapes
of the cinders 56 are unclear, it is preferred that the individual open
shapes of the cutout portions 338 be set smaller than the smallest width
dimension of the agent before combustion when the agent before combustion
is seen from various directions.

[0177] <Action and Effects of Fourth Embodiment>

[0178] In the embodiment with the configurations described above, when the
gas generator 20 is actuated, the gas is produced by the gas generator 20
and the agent such as a gas-generating agent is combusted, and the
cinders 56 of the agent are released into the inside of the cylinder 12
together with the gas. Here, the individual open shapes of the gaps 318
formed between the inner peripheral surface of the attachment hole 54 and
the outer peripheral surface of the insertion portion body 316 excluding
the corner portions are set smaller than the open shape of the gas flow
rate adjusting hole 60, but the sum total of the open areas of all of the
gaps 318 is larger than the open area of the gas flow rate adjusting hole
60. Moreover, the sum total of the open areas of all of the cutout
portions 338 on the outer peripheral side of the peripheral wall 334 is
larger than the open area of the gas flow rate adjusting hole 60.

[0179] Moreover, the gaps 318 and the cutout portions 338 are formed in
four places in the range of the insertion portion body 316 and,
particularly in the present embodiment, every 90 degrees centered on the
axial direction of the insertion portion 316. For this reason, even if
any of the gaps 318 or cutout portions 338 become blocked by the cinders
56, any of the other gaps 318 or cutout portions 338 do not become
blocked by the cinders 56. For this reason, even if the cinders 56 block
any of the gaps 318 or cutout portions 338, the difference between the
sum total of the open areas of the gaps 318 or cutout portions 338 not
blocked by the cinders 56 and the open area of the gas flow rate
adjusting hole 60 becomes smaller, but the gas with the flow rate decided
by the open area of the gas flow rate adjusting hole 60 can be released.

[0180] That is, in the present embodiment also, basically effects that are
the same as those in each of the embodiments heretofore described can be
obtained.

[0181] Moreover, the distal end side of the plug 312 fitted into the
attachment hole 54 is the small diameter portion 322, and the length of
the diagonal lines of the small diameter portion 322 is shorter than the
diameter dimension of the inner peripheral portion of the attachment hole
54. For this reason, when the plug 312 is fitted into the attachment hole
54, the small diameter portion 322 can be simply inserted into the
attachment hole 54. After the small diameter portion 322 is inserted into
the attachment hole 54 in this way, next the tapered portion 320 is
inserted into the attachment hole 54, but the lengths of the diagonal
lines of the tapered portion 320 gradually become longer toward the
insertion portion body 316 side.

[0182] For this reason, the tapered portion 320 is inserted into the
inside of the attachment hole 54 while the corner portions of the tapered
portion 320 interfere with the inner peripheral portion of the attachment
hole 54, whereby eventually the central axis of the insertion portion
body 316 and the central axis of the attachment hole 54 can be aligned
and the insertion portion body 316 can be easily fitted into the
attachment hole 54. When the insertion portion body 316 is fitted into
the attachment hole 54 in this way, the corner portions of the insertion
portion body 316 press against the inner peripheral portion of the
attachment hole 54, so the plug 312 can be held in the piston body 24 by
the friction between the inner peripheral portion of the attachment hole
54 and the corner portions of the insertion portion body 316 without
having to use special fixing means or holding means.

[0183] In the present embodiment, the gaps 318 formed between the inner
peripheral surface of the attachment hole 54 and the outer peripheral
surface of the insertion portion body 316 excluding the corner portions
are used as the vent portions. However, the cutout portions 338 may be
used as the vent portions by the open dimension of each of the cutout
portions 338 along the circumferential direction of the head portion 332
in the outer peripheral surface of the peripheral wall 334 and the open
dimension of each of the cutout portions 338 along the axial direction of
the head portion 332 may also be appropriately set.